Chapter 9 Fundamentals of Genetics Standards SPI 3210.4.4: Determine the probability of a particular trait in an offspring based on the genotype and the

Chapter 9 Fundamentals of Genetics

Standards

SPI 3210.4.4: Determine the probability of a particular trait in an offspring based on the genotype and the particular mode of inheritance.

SPI 3210.4.5: Apply the pedigree data to interpret various modes of genetic dominance.

Fundamentals of GeneticsChapter 9

Table of Contents

Section 1 Mendel’s Legacy

Section 2 Genetic Crosses

Section 1 Mendel’s LegacyChapter 9

Objectives

• Describe how Mendel was able to control how his pea plants were pollinated.

• Describe the steps in Mendel’s experiments on true-breeding garden peas.

• Distinguish between dominant and recessive traits.

• State two laws of heredity that were developed from Mendel’s work.

• Describe how Mendel’s results can be explained by scientific knowledge of genes and chromosomes.


Gregor Mendel

• The study of how characteristics are transmitted from parents to offspring is called genetics.


Gregor Mendel, continued

• Mendel’s Garden Peas– Mendel observed characteristics of pea plants. – Traits are genetically determined variants of a

characteristic.– Each characteristic occurred in two contrasting

traits.


Gregor Mendel, continued

• Mendel’s Methods

– Mendel used cross-pollination techniques in which pollen is transferred between flowers of two different plants.


Mendel’s Experiments

• Mendel bred plants for several generations that were true-breeding for specific traits and called these the P generation.

• Offspring of the P generation were called the F1 generation.

• Offspring of the F1 generation were called the F2 generation.

Chapter 9

Three Steps of Mendel’s Experiments


Chapter 9

Click below to watch the Visual Concept.

Mendel’s Experiments



Mendel’s Results and Conclusions

• Recessive and Dominant Traits

– Mendel concluded that inherited characteristics are controlled by factors that occur in pairs.

– In his experiments on pea plants, one factor in a pair masked the other. The trait that masked the other was called the dominant trait. The trait that was masked was called the recessive trait.


Mendel’s Results and Conclusions, continued

• The Law of Segregation

– The law of segregation states that a pair of factors is segregated, or separated, during the formation of gametes.


Mendel’s Results and Conclusions, continued

• The Law of Independent Assortment

– The law of independent assortment states that factors for individual characteristics are distributed to gametes independent of one another.

– The law of independent assortment is observed only for genes that are located on separate chromosomes or are far apart on the same chromosome.


Support for Mendel’s Conclusions

• We now know that the factors that Mendel studied are alleles, or alternative forms of a gene.

• One allele for each trait is passed from each parent to the offspring.

Chapter 9


Mendel’s Conclusions


Chapter 9 Fundamentals of Genetics

Standards

SPI 3210.4.4: Determine the probability of a particular trait in an offspring based on the genotype and the particular mode of inheritance.

SPI 3210.4.5: Apply the pedigree data to interpret various modes of genetic dominance.

Section 2 Genetic CrossesChapter 9

Objectives• Differentiate between the genotype and the phenotype of an

organism.

• Explain how probability is used to predict the results of genetic crosses.

• Use a Punnett square to predict the results of monohybrid and dihybrid genetic crosses.

• Explain how a testcross is used to show the genotype of an individual whose phenotype expresses the dominant trait.

• Differentiate a monohybrid cross from a dihybrid cross.


Genotype and Phenotype

• The genotype is the genetic makeup of an organism.

• The phenotype is the appearance of an organism.


Probability

• Probability is the likelihood that a specific event will occur.

• A probability may be expressed as a decimal, a percentage, or a fraction.

Chapter 9


Calculating Probability



Predicting Results of Monohybrid Crosses

• A Punnett square can be used to predict the outcome of genetic crosses.

• A cross in which one characteristic is tracked is a monohybrid cross.

Chapter 9


Punnett Square with Homozygous Cross


Chapter 9

Monohybrid Cross of Heterozygous Plants



Predicting Results of Monohybrid Crosses, continued

• A testcross, in which an individual of unknown genotype is crossed with a homozygous recessive individual, can be used to determine the genotype of an individual whose phenotype expresses the dominant trait.

Chapter 9


Testcross




• Complete dominance occurs when heterozygous individuals and dominant homozygous individuals are indistinguishable in phenotype.



• Incomplete dominance occurs when two or more alleles influence the phenotype and results in a phenotype intermediate between the dominant trait and the recessive trait.



• Codominance occurs when both alleles for a gene are expressed in a heterozygous offspring.


Predicting Results of Dihybrid Crosses

• A cross in which two characteristics are tracked is a dihybrid cross.

Chapter 9

Dihybrid Crosses


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Chapter 9 Fundamentals of Genetics Standards SPI 3210.4.4: Determine the probability of a particular trait in an offspring based on the genotype and the